Opacity is a measurement of the degree of non-transparency of a gas stream. This measurement is required and regulated by most states for any industry which has any significant size exhaust stack emission to the atmosphere. A major group that is affected by this regulation, the purpose of which is to minimize the amount of particulate matter in the emissions, is the power industry. (This is based on BTU per hour and varies from state to state.) Most coal-fired and oil-fired power plants must monitor the amount of opacity in their stack emissions. However, current opacity monitors available require a great amount of maintenance to insure the acquisition of valid data. Current federal regulations require that opacity monitors produce valid data for 90% of the time. Many of the opacity monitors now in use require the full time attention of service personnel to achieve this level of data.
Opacity monitors work on the basis of a light beam which is directed horizontally across an exhaust stack or duct to a receiver on the opposite side. An example of such a monitor is described in U.S. Pat. No. 4,647,780 to Dunkel. The light beam continuously sent across is received by a lens and opacity is determined based upon a reading periodically taken. The receiver converts the intensity of the light beam received into an opacity reading based upon its difference from the known intensity of the transmitted beam. The more particulate matter present in the exhaust stream, the higher the opacity monitor reading. One of the problems with opacity meters is that the lens gets dirty with the accumulation of particulate matter from the exhaust gas stream and thus alters the opacity monitor reading. Traditionally the solution to this problem has been to have an instrument person manually wipe the lens clean at periodic times, usually several times per day. This approach has two drawbacks. First, an instrument person is needed to wipe the lens off. This may require calling him or her out in the middle of the night due to the fact that many power stations only work with a day shift instrument crew. Second, between cleanings the monitor may be giving falsely high readings. An alternate approach is to adjust the output of the opacity monitor in order to compensate for the build up of particulate matter on the lens. This approach still requires a person to manually wipe the lens off at some particular time. Air blowers across the lens, as in Dunkel, have been used but are ineffective in keeping the lens sufficiently clean over an extended period of time.
It is no minor task to perform the manual cleaning operation because of the location of the monitors, which are usually located on the stack as high as 91 m (300 feet). The time involved in such operations can be at least one hour to reach the monitors, clean the lens, and reassemble the monitor. As an additional concern, the monitor must be correctly calibrated so as to further provide for accurate readings. Due to vibrational effects the light beam may become misaligned and not fall directly on the receiver lens. Since it is a requirement that these monitors produce valid data 90% of the time, with readings obtained about once every 30 seconds, such operations can considerably reduce the available amount of time during which valid data can be obtained. Failure to satisfy these requirements and regulations could result in heavy fines being levied against the fossil fuel power plant operators.
It is therefore an object of the present invention to provide a method and apparatus for increasing the percentage of valid opacity monitor readings so as to reduce the possibility of having to pay regulatory fines.
It is another object of the present invention to provide a mechanical device to continually clean an opacity monitor which would not interfere with the acquisition of valid opacity monitor readings.